T-box 21 transcription factor is responsible for distorted T(H)2 differentiation in human peripheral CD4+ T cells

Genomic, Epigenomic, Transcriptomic, Proteomic and Metabolomic Approaches in Atopic Dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease with a high prevalence in the developed countries. It is associated with atopic and non-atopic diseases, and its close correlation with atopic comorbidities has been genetically demonstrated. One of the main roles of genetic studies is to comprehend the defects of the cutaneous barrier due to filaggrin deficit and epidermal spongiosis. Recently, epigenetic studies started to analyze the influence of the environmental factors on gene expression. The epigenome is considered to be a superior second code that controls the genome, which includes alterations of the chromatin. The epigenetic changes do not alter the genetic code, however, changes in the chromatin structure could activate or inhibit the transcription process of certain genes and consequently, the translation process of the new mRNA into a polypeptide chain. In-depth analysis of the transcriptomic, metabolomic and proteomic studies allow to unravel detailed mechanisms that cause AD. The extracellular space and lipid metabolism are associated with AD that is independent of the filaggrin expression. On the other hand, around 45 proteins are considered as the principal components in the atopic skin. Moreover, genetic studies based on the disrupted cutaneous barrier can lead to the development of new treatments targeting the cutaneous barrier or cutaneous inflammation. Unfortunately, at present, there are no target therapies that focus on the epigenetic process of AD. However, in the future, miR-143 could be an important objective for new therapies, as it targets the miR-335:SOX axis, thereby restoring the miR-335 expression, and repairing the cutaneous barrier defects.

The association between diabetes and obesity with Dengue infections

Dengue, an arboviral disease is a global threat to public health as the number of Dengue cases increases through the decades and this trend is predicted to continue. Non-communicable diseases such as diabetes and obesity are also on an upward trend. Moreover, past clinical studies have shown comorbidities worsen the clinical manifestation of especially Severe Dengue. However, discussion regarding the underlying mechanisms regarding the association between these comorbidities and dengue are lacking. The hallmark of Severe Dengue is plasma leakage which is due to several factors including presence of pro-inflammatory cytokines and dysregulation of endothelial barrier protein expression. The key factors of diabetes affecting endothelial functions are Th1 skewed responses and junctional-related proteins expression. Additionally, obesity alters the lipid metabolism and immune response causing increased viral replication and inflammation. The similarity between diabetes and obesity individuals is in having chronic inflammation resulting in endothelial dysfunction. This review outlines the roles of diabetes and obesity in severe dengue and gives some insights into the plausible mechanisms of comorbidities in Severe Dengue.

Genetic and Epigenetic Aspects of Atopic Dermatitis

Atopic dermatitis is a heterogeneous disease, in which the pathogenesis is associated with mutations in genes encoding epidermal structural proteins, barrier enzymes, and their inhibitors; the role of genes regulating innate and adaptive immune responses and environmental factors inducing the disease is also noted. Recent studies point to the key role of epigenetic changes in the development of the disease. Epigenetic modifications are mainly mediated by DNA methylation, histone acetylation, and the action of specific non-coding RNAs. It has been documented that the profile of epigenetic changes in patients with atopic dermatitis (AD) differs from that observed in healthy people. This applies to the genes affecting the regulation of immune response and inflammatory processes, e.g., both affecting Th1 bias and promoting Th2 responses and the genes of innate immunity, as well as those encoding the structural proteins of the epidermis. Understanding of the epigenetic alterations is therefore pivotal to both create new molecular classifications of atopic dermatitis and to enable the development of personalized treatment strategies.

In utero priming of highly functional effector T cell responses to human malaria

Malaria remains a significant cause of morbidity and mortality worldwide, particularly in infants and children. Some studies have reported that exposure to malaria antigens in utero results in the development of tolerance, which could contribute to poor immunity to malaria in early life. However, the effector T cell response to pathogen-derived antigens encountered in utero, including malaria, has not been well characterized. Here, we assessed the frequency, phenotype, and function of cord blood T cells from Ugandan infants born to mothers with and without placental malaria. We found that infants born to mothers with active placental malaria had elevated frequencies of proliferating effector memory fetal CD4⁺ T cells and higher frequencies of CD4⁺ and CD8⁺ T cells that produced inflammatory cytokines. Fetal CD4⁺ and CD8⁺ T cells from placental malaria-exposed infants exhibited greater in vitro proliferation to malaria antigens. Malaria-specific CD4⁺ T cell proliferation correlated with prospective protection from malaria during childhood. These data demonstrate that placental malaria is associated with the generation of proinflammatory malaria-responsive fetal T cells. These findings add to our current understanding of fetal immunity and indicate that a functional and protective pathogen-specific T cell response can be generated in utero.

Identification of biomarker sets for predicting the efficacy of sublingual immunotherapy against pollen-induced allergic rhinitis

Sublingual immunotherapy (SLIT) is effective against allergic rhinitis, although a substantial proportion of individuals is refractory. Herein, we describe a predictive modality to reliably identify SLIT non-responders (NRs). We conducted a 2-year clinical study in 193 adult patients with Japanese cedar pollinosis, with biweekly administration of 2000 Japanese allergy units of cedar pollen extract as the maintenance dose. After identifying high-responder (HR) patients with improved severity scores and NR patients with unchanged or exacerbated symptoms, differences in 33 HR and 34 NR patients were evaluated in terms of peripheral blood cellular profiles by flow cytometry and serum factors by ELISA and cytokine bead array, both pre- and post-SLIT. Improved clinical responses were seen in 72% of the treated patients. Pre-therapy IL-12p70 and post-therapy IgG1 serum levels were significantly different between HR and NR patients, although these parameters alone failed to distinguish NR from HR patients. However, the analysis of serum parameters in the pre-therapy samples with the Adaptive Boosting (AdaBoost) algorithm distinguished NR patients with high probability within the training data set. Cluster analysis revealed a positive correlation between serum Th1/Th2 cytokines and other cytokines/chemokines in HR patients after SLIT. Thus, processing of pre-therapy serum parameters with AdaBoost and cluster analysis can be reliably used to develop a prediction method for HR/NR patients.

Both inflammatory and regulatory cytokine responses to malaria are blunted with increasing age in highly exposed children

Background

Young children are at greatest risk for malaria-associated morbidity and mortality. The immune response of young children differs in fundamental ways from that of adults, and these differences likely contribute to the increased susceptibility of children to severe malaria and to their delayed development of immunity. Elevated levels of pro-inflammatory cytokines and chemokines in the peripheral blood during acute infection contribute to the control of parasitaemia, but are also responsible for much of the immunopathology seen during symptomatic disease. Clinical immunity to malaria may depend upon the ability to regulate these pro-inflammatory responses, possibly through mechanisms of immunologic tolerance. In order to explore the effect of age on the immune response to malaria and the development of clinical immunity, cytokines and chemokines were measured in the plasma of children at day 0 of an acute malaria episode and during convalescence.

Results

Younger children presenting with acute malaria exhibited much higher levels of TNF, IL2, and IL6, as well as increased Th1 associated chemokines IP10, MIG, and MCP1, compared to older children with acute malaria. Additionally, the regulatory cytokines IL10 and TNFRI were dramatically elevated in younger children compared to older children during acute infection, indicating that regulatory as well as pro-inflammatory cytokine responses are dampened in later childhood.

Conclusions

Together these data suggest that there is a profound blunting of the cytokine and chemokine response to malaria among older children residing in endemic settings, which may be due to repeated malaria exposure, intrinsic age-based differences in the immune response, or both.

Contribution of neuraminidase 3 to the differentiation of induced regulatory T cells

Neuraminidase family enzymes that hydrolyze the terminal sialic acid linkage in biomolecules are involved in various immune responses. We previously showed that Th1 and Th2 cells differentially express several neuraminidases. Herein, the expression of neuraminidases in induced regulatory T (iTreg) cells was investigated in comparison with that in other T-cell subsets. Contrary to the tendency toward higher neuraminidase 1 mRNA expression in in vitro-differentiated Th2 cells, compared to Th1, Th17 and iTreg cells, we observed significantly higher expression of neuraminidase 3 (Neu3) in iTreg cells. Furthermore, the expression of Neu3 in FoxP3⁺ CD62L^- spleen cells was higher than that in FoxP3⁺ CD62L⁺ and FoxP3^- cells. Lentiviral expression of Neu3 in naïve CD4⁺ T cells during the stimulation culture led to upregulation of FoxP3 expression. On the basis of these findings, we conclude that Neu3 contributes to the differentiation of iTreg cells by upregulation of FoxP3.

The Genetics and Epigenetics of Atopic Dermatitis-Filaggrin and Other Polymorphisms

Atopic dermatitis (AD) is a chronic inflammatory skin disease caused by a combination of genetic and environmental factors. Genetic evidences depict a complex network comprising by epidermal barrier dysfunctions and dysregulation of innate and adaptive immunity in the pathogenesis of AD. Mutations in the human filaggrin gene (FLG) are the most significant and well-replicated genetic mutation associated with AD, and other mutations associated with epidermal barriers such as SPINK5, FLG-2, SPRR3, and CLDN1 have all been linked to AD. Gene variants may also contribute to the abnormal innate and adaptive responses found in AD, including mutations in PRRs and AMPs, TSLP and TSLPR, IL-1 family cytokines and receptors genes, vitamin D pathway genes, FCER1A, and Th2 and other cytokines genes. GWAS and Immunochip analysis have identified a total of 19 susceptibility loci for AD. Candidate genes at these susceptibility loci identified by GWAS and Immunochip analysis also suggest roles for epidermal barrier functions, innate and adaptive immunity, interleukin-1 family signaling, regulatory T cells, the vitamin D pathway, and the nerve growth factor pathway in the pathogenesis of AD. Increasing evidences show the modern lifestyle (i.e., the hygiene hypothesis, Western diet) and other environmental factors such as pollution and environmental tobacco smoke (ETS) lead to the increasing prevalence of AD with the development of industrialization. Epigenetic alterations in response to these environmental factors, including DNA methylation and microRNA related to immune system and skin barriers, have been found to contribute to the pathogenesis of AD. Genetic variants and epigenetic alteration might be the key tools for the molecular taxonomy of AD and provide the background for the personalized management.

Polygonum multiflorum Decreases Airway Allergic Symptoms in a Murine Model of Asthma

The root of Polygonum multiflorum (also called He-Shou-Wu in Chinese) is a common herb and medicinal food in Asia used for its anti-aging properties. Our study investigated the therapeutic potential of an extract of the root of Polygonum multiflorum (PME) in allergic asthma by using a mouse model. Feeding of 0.5 and 1 mg/mouse PME inhibited ovalbumin (OVA)-induced allergic asthma symptoms, including airway inflammation, mucus production, and airway hyper-responsiveness (AHR), in a dose-dependent manner. To discern PME's mechanism of action, we examined the profile and cytokine production of inflammatory cells in bronchial alveolar lavage fluid (BALF). We found that eosinophils, the main inflammatory cell infiltrate in the lung of OVA-immunized mice, significantly decreased after PME treatment. Th2 cytokine levels, including interleukin (IL)-4, IL-5, IL-13, eotaxin, and the proinflammatory cytokine tumor necrosis factor (TNF)-[Formula: see text], decreased in PME-treated mice. Elevated mRNA expression of Th2 transcription factor GATA-3 in the lung tissue was also inhibited after oral feeding of PME in OVA-immunized mice. Thus, we conclude that PME produces anti-asthma activity through the inhibition of Th2 cell activation.

Impact of In Utero Exposure to Malaria on Fetal T Cell Immunity

Pregnancy-associated malaria, including placental malaria, causes significant morbidity and mortality worldwide. Recently, it has been suggested that in utero exposure of the fetus to malaria antigens may negatively impact the developing immune system and result in tolerance to malaria. Here, we review our current knowledge of fetal immunity to malaria, focusing on the dynamic interactions between maternal malaria infection, placental development, and the fetal immune system. A better understanding of the long-term impact of in utero malaria exposure on the development of natural immunity to malaria, immune responses to other childhood pathogens, and vaccine immunogenicity is urgently needed. This may guide the implementation of novel chemoprevention strategies during pregnancy and facilitate the push toward malaria vaccines.

Knockdown of T-bet expression in Mart-127-35 -specific T-cell-receptor-engineered human CD4(+) CD25(-) and CD8(+) T cells attenuates effector function

Gene transfer to create tumour epitope-specific cytolytic T cells for adoptive immunotherapy of cancer remains an area of active inquiry. When the Mart-127-35 -specific DMF5 T-cell receptor (TCR) is transferred into peripheral human CD4(+) T cells, the reprogrammed cells exhibit a T helper type 1 (Th1) phenotype with significant multifactorial effector capabilities. The T-bet transcription factor plays an important role in determination of the Th1 differentiation pathway. To gain a deeper understanding of how T-bet controls the outcome of human T-cell reprogramming by gene transfer, we developed a system for examining the effects of short hairpin RNA-mediated T-bet gene knockdown in sorted cell populations uniformly expressing the knockdown construct. In this system, using activated peripheral human CD4(+)  CD25(-) and CD8(+) T cells, T-bet knockdown led to attenuation of the interferon-γ response to both antigen-specific and non-specific TCR stimulation. The interleukin-2 (IL-2) antigen-specific response was not attenuated by T-bet knockdown. Also, in TCR-reprogrammed CD8(+) cells, the cytolytic effector response was attenuated by T-bet knockdown. T-bet knockdown did not cause redirection into a Th2 differentiation pathway, and no increased IL-4, IL-10, or IL-17 response was detected in this system. These results indicate that T-bet expression is required for maintenance of the CD4(+)  CD25(-) and CD8(+) effector phenotypes in TCR-reprogrammed human T cells. They also suggest that the activation protocol necessary for transduction with retrovectors and lentivectors may commit the reprogrammed cells to the Th1 phenotype, which cannot be altered by T-bet knockdown but that there is, nevertheless, a continuous requirement of T-bet expression for interferon-γ gene activation.

Neonatal immunology: responses to pathogenic microorganisms and epigenetics reveal an "immunodiverse" developmental state

Neonatal animals have heightened susceptibility to infectious agents and are at increased risk for the development of allergic diseases, such as asthma. Experimental studies using animal models have been quite useful for beginning to identify the cellular and molecular mechanisms underlying these sensitivities. In particular, results from murine neonatal models indicate that developmental regulation of multiple immune cell types contributes to the typically poor responses of neonates to pathogenic microorganisms. Surprisingly, however, animal studies have also revealed that responses at mucosal surfaces in early life may be protective against primary or secondary disease. Our understanding of the molecular events underlying these processes is less well developed. Emerging evidence indicates that the functional properties of neonatal immune cells and the subsequent maturation of the immune system in ontogeny may be regulated by epigenetic phenomena. Here, we review recent findings from our group and others describing cellular responses to infection and developmentally regulated epigenetic processes in the newborn.

Establishment of monoclonal antibodies against a novel eosinophil-specific cell surface molecule, major facilitator super family domain containing 10

Eosinophilic inflammation is the prominent feature of bronchial asthma, though the importance of eosinophils in the pathogenesis of this disease is controversial. We here established monoclonal antibodies against a newly identified cell surface molecule specifically expressed on mouse eosinophils. Eosinophils were highly purified from small intestine lamina propria and thymus as CD11c(+)Gr1(low)F4/80(+)B220(-) cells. Upon comparative microarray analysis for mRNA expressed in eosinophils and other leukocytes, major facilitator super family domain containing 10 (Mfsd10) was identified as a novel eosinophil-specific cell surface molecule. Hybridomas were established from spleen cells of rats immunized with Mfsd10-introduced Ba/F3 cells. One of three monoclonal antibodies against Mfsd10 displayed selective binding activity against eosinophils recovered in bronchoalveolar lavage fluid of ovalbumin-immunized and -challenged mice. Administration of this antibody in vivo induced a significant reduction of eosinophils recruited in the allergic lungs. Anti-Mfsd10 antibody is useful for investigating the pathophysiological roles of eosinophils with its selective binding and neutralizing activity for mouse eosinophils.

Protein phosphatase 1 is involved in IL-2-induced IL-5 and IL-13 expression in human T cells

IL-2 plays an important role in immunological and other biological functions. This cytokine directly induces the production of several cytokines, such as IL-5 and IL-13. The mechanisms of IL-2-mediated cytokine synthesis are mostly unclear; however, the involvement of IL-2 receptor (IL-2R)β has been suggested. In this study, the signaling molecule downstream of IL-2Rβ was investigated, employing a proteomic approach. Full-length IL-2Rβ and its mutant in which the intracellular component was truncated were introduced in an IL-2Rα- and IL-2Rγ-stably transfected T cell hybridoma, S1. The differential phosphorylation profiles of protein tyrosine residues in these cells upon IL-2 stimulation were examined by two-dimensional gel electrophoresis. The candidate phosphoproteins of interest were re-covered, in-gel digested and mass spectrometry fingerprinted. Among proteins specifically phosphorylated in full-length IL-2Rβ-expressing cells in response to IL-2 stimulation, protein phosphatase (PP)1β and FK506-binding protein 4 were identified. Particularly, PP1β augmented IL-5 and IL-13 expression stimulated by IL-2 but not by anti-CD3 antibody in human peripheral CD4+ T cells upon ectopic expression. IL-2-induced cytokine expression was suppressed by overexpression of PP1 regulatory subunit 2. A PP1 inhibitor, tautomycin, but not a PP2A inhibitor, okadaic acid, also inhibited the IL-2R-mediated responses. It was conclusively shown that PP1 is crucially involved in IL-2-mediated IL-5 and IL-13 synthesis in human T cells.

The association between IFN-γ and IL-4 genetic polymorphisms and childhood susceptibility to bronchial asthma

The present study aims to investigate the association between the genetic polymorphisms of interferon (IFN)-γ and interleukin (IL)-4 with childhood susceptibility to asthma and the levels of IFN-γ, IL-4, and immunoglobulin (Ig) E among asthmatic children. A total of 100 asthmatic children and 122 control children were enrolled in the present study. The genotypes of the IFN-γ gene at the -179G/T locus and the IL-4 gene at the -33C/T and -589C/T loci were detected using polymerase chain reaction with restriction fragment length polymorphism. The IFN-γ gene at the +874A/T locus and the IFN-γ CA repeats were tested using allele-specific and capillary electrophoresis, respectively, whereas the IFN-γ, IL-4, and total IgE levels were measured using enzyme-linked immunosorbent assays. The 100 asthmatic children and the 122 control children were all GG homozygous in the -179 locus of the IFN-γ gene, which shows that the IFN-γ gene is not mutated at the -179 locus. No significant differences were found in terms of genotypic and allelic frequency distribution in the IFN-γ gene or the CA repeat at the +874A/T locus between the asthmatic children and the control (P>0.05). An association was found between the polymorphism of the IFN-γ gene at +874A/T and IFN-γ levels. IFN-γ expression was lower among patients with the AA genotype than those with the AT genotype (P<0.05); the genotypic and allelic frequency distributions of the IL-4 gene at -33C/T and -589C/T were significantly different between the asthmatic children and the control (P<0.05). The levels of IL-4 and IgE among children with TT genotype at the -33 and -589 loci were higher than those with the CT genotype, but only the polymorphism at -33C/T was associated with IL-4 levels (P<0.05). The polymorphisms of the IFN-γ gene at +874A/T or the CA repeats are not correlated with susceptibility to asthma. Thus, the polymorphism at +874A/T is correlated with IFN-γ level. The TT genotypes of the IL-4 gene at the -33 and -589 loci are associated with asthma susceptibility in children, and polymorphism at the -33 locus may be associated with IL-4 level.

Selective down-regulation of Th2 cell-mediated airway inflammation in mice by pharmacological intervention of CCR4

BACKGROUND

The chemokine receptor CCR4 has been implicated in Th2 cell-mediated immune responses. However, other T cell subsets are also known to participate in allergic inflammation.

OBJECTIVE

The role of CCR4 in Th1, Th2, and Th17 cell-mediated allergic airway inflammation was investigated.

METHOD

We generated an allergic airway inflammation model by adoptive transfer of in vitro-polarized ovalbumin (OVA)-specific Th1, Th2, and Th17 cells. The effect of a low-molecular weight CCR4 antagonist, Compound 22, on this model was examined.

RESULTS

Upon in vitro polarization of DO11.10 naïve T cells, Th1- and Th2-polarized cells dominantly expressed CXCR3 and CCR4, respectively, while Th17-polarized cells expressed CCR6 and CCR4. Intranasal OVA-challenge of mice transferred with each T cell subset induced accumulation of T cells in the lungs. Eosinophils were also massively accumulated in Th2-transferred mice, whereas neutrophils were preferentially recruited in Th1- and Th17-transferred mice. Compound 22, as well as anti-CCL17 or anti-CCL22 antibody selectively suppressed accumulation of Th2 cells and eosinophils in the lungs of Th2-transferred and OVA-challenged mice. Compound 22 also inhibited bronchial hyperresponsiveness but had little effect on goblet cell hyperplasia in Th2-transferred and OVA-challenged mice.

CONCLUSIONS AND CLINICAL RELEVANCE

There were notable differences in allergic lung inflammation mediated by different T cell subsets. CCR4 blockage was selectively effective for suppression of Th2-mediated allergic inflammation by blocking infiltration of Th2 cells.

A common promoter variant of TBX21 is associated with allele specific binding to Yin-Yang 1 and reduced gene expression

T-bet is a key regulator for the lineage commitment in CD4 T helper (Th) 1 cells by activating the hallmark production of interferon-γ, and its expression level is linked to autoimmune, infectious, and allergic diseases. A T to C base substitution has been identified at position -1993 in the TBX21 (encoding T-bet) promoter and has been associated with asthma and systemic lupus erythematosus. This study aimed to investigate the molecular mechanisms responsible for the influence of the T-1993C polymorphism on transcription and its functional effect by luciferase reporter, EMSAs, Chromatin immunoprecipitation assay, and flow cytometric analysis of intracellular T-bet, IFN-γ and IL-4 expression in activated CD4(+) T cells. The presence of a -1993T allele obviously increases promoter activity compared with that of a promoter with a -1993C allele. TBX21 promoter carrying -1993C allele possesses significantly stronger binding affinity to the Yin Yang 1 (YY1) transcription factor than that carrying -1993T allele. YY1 overexpression decreased TBX21 promoter function in a T cell line, demonstrating that this element functions as a repressor. The C to T base exchange relieves the repression mediated by YY1. The individuals carrying -1993C allele were determined to have significantly diminished expression of TBX21 and IFN-γ and increased IL-4 production in cells compared with the individuals carrying -1993T allele (P < 0.05). These findings demonstrate that the TBX21 T-1993C polymorphism represses TBX21 expression and Th1 cytokine production through control of YY1, which might result in the imbalance between Th1 and Th2 immune responses in autoimmune or allergic diseases.

Zinc finger protein, multitype 1, suppresses human Th2 development via downregulation of IL-4

BACKGROUND

Among several GATA family transcription factor-associating proteins, zinc finger protein, multitype 1 (ZFPM1), at least that of murine origin, has been shown to modulate the activity of GATA-3. However, the functional role of human ZFPM1 in the immune system has not been elucidated. Therefore, we here investigated the contribution of ZFPM1 to human Th1/Th2 differentiation.

METHODS

The cDNA of ZFPM1 was cloned and introduced into human cord blood CD4+ T cells by a lentiviral transduction system. Then, the expression of IL-4 and IFN-γ mRNA was determined by quantitative real-time RT-PCR. The effect of ZFPM1 on the promoter activity of IL-4 and IFN-γ in Jurkat cells was also investigated.

RESULTS

Stimulation-induced expression of IL-4 and IFN-γ in human CD4+ T cells was suppressed and enhanced, respectively, by the introduction of ZFPM1. The transcriptional activity of IL-4 was also diminished by ZFPM1, whereas that of IFN-γ was not affected.

CONCLUSION

ZFPM1 that facilitates human Th1 differentiation via the downregulation of IL-4 is a potential target for the treatment of allergic diseases.

Adaptive immunity

The innate immune system provides critical mechanisms for the rapid sensing and elimination of pathogens. Adaptive immunity has evolved to provide a broader and more finely tuned repertoire of recognition for both self- and nonself-antigens. Adaptive immunity involves a tightly regulated interplay between antigen-presenting cells and T and B lymphocytes, which facilitate pathogen-specific immunologic effector pathways, generation of immunologic memory, and regulation of host immune homeostasis. Lymphocytes develop and are activated within a series of lymphoid organs comprising the lymphatic system. During development, sets of gene segments are rearranged and assembled to create genes encoding the specific antigen receptors of T and B lymphocytes. The rearrangement mechanism generates a tremendously diverse repertoire of receptor specificities capable of recognizing components of all potential pathogens. In addition to specificity, another principal feature of adaptive immunity is the generation of immunologic memory. During the first encounter with an antigen (pathogen), sets of long-lived memory T and B cells are established. In subsequent encounters with the same pathogen, the memory cells are quickly activated to yield a more rapid and robust protective response.